It is the central thesis of this proposal that both ACh and DA modulate the properties of the voltage- dependent sodium conductance in the hippocampus and that these effects are mediated via convergence of the cAMP-dependent protein kinase (PKA)- and protein kinase C (PKC)-dependent regulatory pathways. Further, we propose that PKC and PKA mediate their effects through direct phosphorylation of the sodium channel alpha subunit. The proposed experiments test these hypotheses in acutely isolated hippocampal pyramidal neurons and in stably transfected Chinese Hamster Ovary (CHO) cell lines using techniques which first isolate specific conductances and by then measuring single or multi-channel ionic currents while controlling for biologically relevant variables such as the transmembrane voltage and the biochemical composition of the intra- and extracellular environment. This proposal has four specific aims: 1. To complete the ongoing characterization of regulation of Na conductance in rat hippocampal pyramidal neurons by muscarinic acetylcholine receptors acting through PKC. 2. To determine how DA receptors or other receptors coup;led to activation and inhibition of AC modulate Na conductance in hippocampal pyramidal neurons through PKA. 3. To determine the degree and mechanism of convergence of these two signalling pathways. 4. To analyze the molecular mechanism of regulation by these pathways.